The invention relates to a method of forming a metal wire in a semiconductor device, and more particularly, to a method of forming a metal wire in a semiconductor device that enhances the reliability of the device.
In the method of forming a metal wire in a semiconductor device, a damascene method using tungsten as a plug is employed. As the device becomes highly integrated, even though the design rule is reduced, a high driving ratio is required. Thus, a metal wire forming method using metal material having a low specific resistance and a low dielectric material (low-k) has been studied.
In general, when the metal wire is formed using a copper damascene, the process of forming the metal wire has the following drawbacks:
First, the electrons are transported mainly in metals having a low specific resistance. If the thickness of a barrier metal layer formed on the bottom portion of a contact connecting a first metal wire and a second metal wire is thick, then the transport of electrons through a copper wire having a low specific resistance is decreased. By decreasing the amount of transported electrons, copper ions diffuse into an insulating layer so that a void is generated, ions penetrate the insulating layer, and vacancies are created. Due to the above phenomenon, the metal wire breaks due to an electro-migration (EM) failure or a stress-migration (SM) failure.
Second, since copper has a large affinity for oxygen, copper is significantly oxidized when exposed at an exterior surface. This increases the a resistance of the metal layer.
Third, characteristics such as RC delay, leakage current, and time dependent dielectric breakdown are degraded by the above mentioned problems. Thus, there is a problem with the driving ratio of the device and it is difficult to reduce the size of the device.